The prior art discloses processes for improving adhesion properties of polyolefin films, in particular polypropylene films. These films are usually plasma, flame or corona-treated on one or both surfaces during production. These processes increase the surface tension of the film and improve, for example, its printability, metallizability or adhesion to other coatings.
The disadvantage of these known processes is that the increased surface tension drops continuously after the film has been produced. By the time the film is processed, the surface tension has frequently dropped so much that a further surface treatment must be carried out before printing, metallization or other corresponding processing steps in order to ensure the desired good adhesive strength. Due to the subsequent treatment, however, the original values are no longer achieved. Correspondingly, the adhesion properties of these films or the adhesion properties achieved by this process are in need of improvement.
In order to improve the adhesive strength by other methods, films are provided with a topcoat of acrylates before processing or printing. Although these coatings ensure the desired service properties, they are, however, at the same time associated with additional working steps, which are economically unacceptable for many areas of application for cost reasons.
The object of the present invention was therefore to provide a polyolefin film which is distinguished by particularly good adhesion properties. In particular, good adhesion to water-based printing inks is particularly desirable. The film should be economic and inexpensive to produce. The other film service properties required must not be impaired.